Annular barrier with passive pressure compensation

Abstract

The present invention relates to an annular barrier to be expanded in an annulus between a well tubular structure and an inside wall of a borehole downhole for providing zone isolation between a first zone and a second zone of the borehole, the annular barrier comprising a tubular metal part for mounting as part of the well tubular structure, an expandable sleeve surrounding the tubular metal part and having an inner face facing the tubular metal part and an outer face facing the inside wall of the borehole, each end of the expandable sleeve being connected with the tubular metal part, and an annular space between the inner face of the expandable sleeve and the tubular metal part, wherein the tubular part and the inner face of the expandable sleeve substantially hermetically enclose the annular space, the annular space comprising a compound adapted to expand the annular space, and wherein the expandable sleeve comprises two first sections abutting the ends of the expandable sleeve and a second section between the first sections, the first section of the expandable sleeve has a first inner diameter in an unexpanded condition of the annular barrier, and the second section of the expandable sleeve has a second inner diameter in the unexpanded condition, which second inner diameter is larger than the first inner diameter in the unexpanded condition, or the first sections have a first thickness which is larger than a second thickness of the second section in the unexpanded condition. Furthermore, the invention relates to a downhole system and a method of expanding an annular barrier.

The invention claimed is: 
     
       1. An annular barrier to be expanded in an annulus between a well tubular structure and a wall of a borehole downhole for providing zone isolation between a first zone and a second zone of the borehole, the annular barrier comprising:
 a tubular metal part for mounting as part of the well tubular structure, 
 an expandable sleeve surrounding the tubular metal part and having an inner face facing the tubular metal part and an outer face facing the wall of the borehole, each end of the expandable sleeve being connected with the tubular metal part, and 
 an annular space between the inner face of the expandable sleeve and the tubular metal part, 
 wherein the tubular metal part and the inner face of the expandable sleeve substantially hermetically enclose the annular space, the annular space comprising a compound substantially hermetically enclosed in the annular space in an unexpanded condition of the annular barrier, the compound being adapted to expand the annular space while substantially hermetically enclosed in the annular space, and wherein the expandable sleeve comprises two first sections abutting the ends of the expandable sleeve and a second section between the first sections, the first sections and the second section of the expandable sleeve having a one-piece construction, each first section of the expandable sleeve having a first inner diameter in the unexpanded condition of the annular barrier, and the second section of the expandable sleeve having a second inner diameter in the unexpanded condition, which second inner diameter is larger than the first inner diameter in the unexpanded condition, or the first sections have a first thickness which is larger than a second thickness of the second section in the unexpanded condition. 
 
     
     
       2. The annular barrier according to  claim 1 , wherein the first sections have an increasing thickness. 
     
     
       3. The annular barrier according to  claim 1 , wherein the compound comprises at least one thermally decomposable compound adapted to generate gas or super-critical fluid upon decomposition, the thermally decomposable compound decomposing at a temperature below 400° C. 
     
     
       4. The annular barrier according to  claim 1 , wherein the ends of the expandable sleeve are welded to the tubular part. 
     
     
       5. The annular barrier according to  claim 1 , wherein the expandable sleeve comprises a transition section between at least one of the first sections and the second section, the transition section having an increasing thickness from the second section to the first section. 
     
     
       6. The annular barrier according to  claim 1 , wherein the expandable sleeve comprises a third section between the at least one of the first sections and the second section, the third section having a third thickness which is smaller than the first thickness and larger than the second thickness, the third section of the expandable sleeve having the one-piece construction with the first sections and the second section. 
     
     
       7. The annular barrier according to  claim 6 , wherein the expandable sleeve comprises a first transition section between the second section and the third section and a second transition section between the third section and the first section. 
     
     
       8. The annular barrier according to  claim 6 , wherein the third section having the third thickness has a uniform cross-section extending parallel to a longitudinal axis of the expandable sleeve in the unexpanded condition of the annular barrier. 
     
     
       9. The annular barrier according to  claim 1 , wherein the second section is adapted to expand at a first pressure above 300 bar, preferably above 325 bar, more preferably at a pressure of approximately 345 bar, and the first sections are adapted to expand at a second pressure which is higher than the first pressure. 
     
     
       10. The annular barrier according to  claim 1 , wherein the compound comprises nitrogen. 
     
     
       11. The annular barrier according to  claim 1 , wherein the compound is selected from a group consisting of: ammonium dichromate, ammonium nitrate, ammonium nitrite, barium azide, sodium nitrate, or a combination thereof. 
     
     
       12. The annular barrier according to  claim 1 , wherein the compound is present in the form of a powder, a powder dispersed in a liquid or a powder dissolved in a liquid. 
     
     
       13. The annular barrier according to  claim 1 , further comprising a heating wire arranged in the tubular metal part or in an abutment to the tubular metal part. 
     
     
       14. A downhole system comprising:
 the well tubular structure, and 
 the annular barrier according to  claim 1 . 
 
     
     
       15. The downhole system according to  claim 14  further comprising a plurality of annular barriers. 
     
     
       16. The downhole system according to  claim 14 , wherein the well tubular structure is filled with a fluid having a temperature above 110° C., preferably a temperature above 180° C., and more preferably a temperature above 250° C. 
     
     
       17. The downhole system according to  claim 14 , further comprising a tool comprising a heating unit for heating the tubular metal part of the annular barrier from within the well tubular structure. 
     
     
       18. The downhole system according to  claim 17 , wherein the tool comprises isolation means for isolating a zone in the well tubular structure opposite the expandable space of the annular barrier. 
     
     
       19. The downhole system according to  claim 17 , wherein the heating unit of the tool comprises a heating wire adapted to be arranged in abutment to the tubular metal part. 
     
     
       20. The downhole system according to  claim 14 , wherein the well tubular structure is connected to a tubing, such as a drill pipe, for submerging the well tubular structure, the tubing being connected with a heating device at surface or seabed. 
     
     
       21. A method of expanding the annular barrier according to  claim 1  comprising:
 activating the compound in the annular space so that the annular space starts to expand, thereby causing the second section of the expandable sleeve to expand by a first pressure, and 
 expanding the first sections of the expandable sleeve if the first pressure exceeds a second pressure. 
 
     
     
       22. The annular barrier according to  claim 1 , wherein the first thickness is at least 50% larger than the second thickness. 
     
     
       23. The annular barrier according to  claim 1 , wherein the tubular metal part does not have any openings, holes, or apertures into the annular space.